Whilst I will not disagree that potions are pretty weak, there comes a problem with making changes that so potions too useful, a problem that occurred back in the early days of WOW: Raid content had to be designed with the assumption potions would be used by all players as often as they could. This means that HP pools of bosses would be increased to keep the level the same, without doing this, you lessen the impact of dps checks, resulting in too many people clearing content too fast. If you do increase the HP pools, players that don't currently chug pots every 5 minutes, will need to start doing so. It's all about balance.